In recent years, automatic focus or autofocus (AF) and automatic exposure (AE) video and still photographic cameras have come into common usage as the cost of integrated circuits, photosensors, and miniaturized servo systems for adjusting the focal length of the imaging lens and controlling the exposure time period have become much less expensive. In addition, the availability of inexpensive microprocessors, RAM and ROM chips, and other microcontroller components has allowed designers to incorporate sophisticated algorithms with active or passive range sensors for AF systems and with multi-segmented photometric sensor arrays for AE systems to provide the user with highly accurate "point and shoot" capabilities. These capabilities have been incorporated in relatively simple range finder photographic cameras and highly complex single lens reflex (SLR) photographic still cameras as well as in video cameras.
The development and incorporation of multi-segmented photosensor integrated circuit arrays for use in photographic still cameras is summarized in commonly assigned U.S. Pat. No. 5,146,258 to Bell et al, incorporated herein by reference in its entirety. The '258 patent discloses an improved multi-segmented photometric sensor coupled to selection circuitry for selecting a combination of the signals derived from each segment of the sensor for setting the exposure conditions of the image captured by the camera. The photometric sensor may also be used in conjunction with an electronic strobe flash for providing a reflected light intensity feedback signal that is processed and employed to set the duration of the flash.
In AF control systems, active or passive range finders have been developed to provide signals from which the distance between the camera body and (typically) the subject or structure in the scene that the user has centered the imaging lens on may be determined and employed with a motorized servo-system to adjust the focal length of the imaging lens. Passive range finders employ one or more pairs of linear photo-diode arrays that are positioned a fixed distance apart which forms the baseline of the autoranging triangulation system. In triangulation AF systems, the baseline is a necessary dimension which allows for the formation of similar triangles used to calculate subject distance. Generally, as the baseline dimension and focal length increases and the linear sensor array width (pitch) decreases, the maximum sensing distance increases.
Typically, a pair of focusing lenses are positioned with respect to each pair of spaced apart linear photosensitive arrays to focus the image the camera is pointed at onto the linear arrays. In SLR camera systems, the focusing lenses are arranged symmetrically with respect to the optical axis of the camera's imaging lens and light passing through the lens (TTL) is diverted by half silvered mirrors through the pair of focusing lenses and onto the linear arrays. In range finder cameras, the pair of focusing lenses and the associated linear arrays of photosensitive elements are mounted on the camera a distance away from the imaging lens.
The photo-electrically converted signals from the photosensitive elements of the linear arrays are processed by the microprocessor based AF control algorithm to detect a displacement of the two images focused thereon and to provide a control signal to a motor which drives a gear mechanism to adjust the imaging lens focus. The operation of a typical AF system is described in U.S. Pat. No. 4,643,557 to Ishizaki et al (incorporated by reference herein in its entirety) and is referred to in the above incorporated '259 patent.
Various efforts have been made to reduce the number of photosensitive components and lensing systems necessary for providing accurate AE, AF and photoflash control by employing signals derived from the segments of the multicell photometric arrays in conjunction with or in substitution for signals developed from the linear arrays of photosensitive elements to fine tune the AE and AF functions as described in the above incorporated '258 and '557 patents. In video cameras, where two dimensional CCD arrays are employed, output signals from selected CCD elements are employed in AF and AE operations as disclosed in commonly assigned U.S. Pat. No. 4,684,995 to Baumeister. After analog to digital conversion, the most significant bit and least significant bit portions of the digitized word corresponding to the analog signal output of the selected CCD elements are employed in automatic focus and exposure adjustments. Simultaneously, the digital word information is processed to develop the recorded video information for each corresponding pixel of the image being recorded.
In a similar fashion, although employing redundant photosensitive elements, U.S. Pat. No. 4,974,007 to Yoshida describes a range sensor of multiple pairs of linear photosensitive element arrays and a multi-segment photometric sensor, where the pairs of linear arrays are spaced so as to coincide with segments of the photometric sensor. The range sensor and photometric sensor are formed on separate IC substrates and are employed in a TTL arrangement within an SLR camera where separate lensing elements image the scene viewed through the imaging lens of the camera onto the respective sensors. The signals developed by the photometric sensor segments and the pairs of linear photosensitive element arrays are combined to provide AF and AE functions, particularly for the automatic exposure control of the flash duration. While the positioning of the linear photosensitive element arrays of the range sensor so that they fall within each segment of the photometric sensor of the '007 Patent may have certain utility in TTL arrangements, the advantages that may be gained thereby in that context are achieved at the cost of substantial reduction in the baseline between respective pairs of linear arrays employed in the AF function.
Despite these advances, problems remain in the integration of the components of the AF and AE systems to achieve miniaturization, low cost and accuracy in both assembly in-camera systems and correlation of the signals derived by the range sensor and photometric sensor elements. In practice, the separate integrated circuit chips on which the photometric sensor arrays and linear range sensor arrays are formed must be precisely aligned during assembly of the camera with the camera imaging lens, the viewfinder optics and with each other. The four alignment operations are time consuming, and alignment errors affect camera AF and AE functions that result in poor quality photo images.